This application claims priority to South Korean Patent Application number 2001-0082601 filed Dec. 21, 2001.
The present invention relates to switching mode power supplies (SMPS) also known as switching power supplies. More specifically, the present invention relates to SMPSs that are capable of burst-mode operation, for example, in a standby or reduced power mode.
Previously developed electronic equipment such as televisions, computer monitors, VCRs, etc., commonly have power supply circuits that may operate in two at least modes. Typically, these may be a normal operation mode in which the equipment consumes full power. There may also be a standby mode in which the equipment waits for a signal to enter normal operation mode. While in standby mode, power consumption is minimized.
In response to growing awareness of environmental problems, electronic equipment is increasingly designed to have at least one function to economize on electric energy consumption. Electronic equipment generally uses less electrical power in standby mode than in normal operation mode, but it typically spends more time in standby mode rather as compared with normal operation mode. Some countries have tightened regulatory control over power consumption levels of some types of electronic equipment when operating in standby mode.
A previously developed piece of electronic equipment typically may use an auxiliary power source or may lower at least one power supply circuit output voltage in order to reduce input power level when operating in standby mode. But the use of such techniques to reduce output power may involve an increase in the number of component parts in a product. Thus, the use of such techniques may tend to increase product cost. Moreover, the amount of reduction of the power consumption in standby mode obtainable through such techniques may be insufficient.
In some applications, for example in consumer grade electronic devices, operation over a wide tolerance in input voltage, using cheaper components, and without performance degradation is desirable. In previously developed circuits, it may be necessary to adjust the level shifting circuit or the scaling circuit if it is required to accommodate wide variations in input supply voltage, for example, in a product variant. Alternatively, optimal performance may be compromised by design constraints, such as of multiple product variants.
U.S. Pat. No. 6,252,783 issued to Huh et al. discloses a SMPS that has two distinct operating modes: a normal mode and a standby mode. In the standby mode, normal switching operation is performed for a predetermined time and then stopped for a second predetermined time continually. Standby mode corresponds to low load, and an output smoothing circuit carries the load during the periods that the switching mode circuit is operating. This type of operation is termed xe2x80x9cburst mode operationxe2x80x9d and conserves energy since switching losses occur intermittently rather than continuously. In the circuits of U.S. Pat. No. 6,252,783, an SMPS has primary and secondary circuits separated by a transformer having primary and secondary windings. The circuits of the SMPS of U.S. Pat. No. 6,252,783 sense a standby mode signal output from a micro-computer in the secondary circuit of a transformer and transfer the result to the primary circuit via an opto-isolating photo-coupler. The photo-coupler provides voltage isolation between circuits associated with the primary and the secondary of the transformer. This use of opto-isolation in an SMPS is, however, relatively expensive. The various reasons for needing such voltage isolation are well known in the art and may have (inter alia) safety, regulatory and EMC (electromagnetic compatibility) aspects.
Accordingly, there is a need for an SMPS that avoids any need for costly components (such as photo-couplers) to signal between primary and secondary transformer circuits while preserving the advantages of the previously developed SMPS designs.
According to an aspect of the invention, a switching power supply having a normal operation mode and a standby operation mode is provided. Embodiments of the switching power supply may include a power supply section, a mode discriminator, control voltage generator and a switching controller. The switching power supply may comprise a power supply section having a main switch coupled to a primary winding of a transformer. The mode discriminator may be operable to generate a mode signal in response to an external sync signal presented at the primary winding of the transformer. The mode discriminator may determine the choice between operation in normal operation mode versus standby operation mode. The voltage generator may determine the output voltage according to the operating mode. The switching controller may operate the main switch continually in normal mode or in intermittent bursts in standby mode.
In various embodiments, the present invention offers a design capable of providing a superior cost-performance tradeoff across variations in power supply, component tolerance and product application and/or design.